The present invention relates to a drive-controlling method for detecting a collision of a driven member, such as a hand or various tool(s), attached onto an arm of a robot serving as a driver with obstacles, and which controls to keep damages of the members from the collision minimum, and the present invention also relates to an drive-controlling apparatus using the method and a robot having the apparatus.
Conventionally, various suggestions have been made for technologies in collision detection of movable parts of an industrial robot with an obstacle during operation. For example, a method for detecting a collision based on waggles of signals from a torque sensor attached on a motor which drives an arm of a robot is disclosed in Japanese Patent Application Laid-Open H5-208394 (1993).
Another method is disclosed in Japanese Patent Application Laid-Open H8-66893 (1996) and Japanese Patent Application Laid-Open H11-70490 (1999). The method is such a way that a disturbance of torque sustained by a servo motor which drives a robot arm is estimated by using an observer.
Still another method is disclosed in Japanese Patent Application Laid-Open H8-229864 (1996). The method is such a way that a collision is detected based on a deviation (or an actual deviation) between an instructed position of a movable part of a robot given by a robot controller and an actual position. More particularly, the method is to calculate a logical deviation of position based on a delay time of control system of the robot, and to detect a collision based on a result of comparison between the logical deviation and the above actual deviation.
Other method for procedures after the collision detection is disclosed in Japanese Patent Application Laid-Open H7-143780 (1995). The method is such a way that a torque is loaded in a direction opposite to that of driving of a motor when a collision is detected so that it cuts down a time between the detection of the collision and a moment at which the collided part of the robot is stopped.
As mentioned above, various suggestions of technologies in detecting a collision of the movable part of the robot with the obstacles and in stopping the collided part of the robot after the collision is detected have been made conventionally. However, those suggestions are not sufficient in terms of reducing the degree of damage which the members suffer from the collision. In other words, since just stopping the robot, after the collision is detected, only results in the movable part of the robot pushing against the obstacle for a certain time, it cannot reduce the impact of the collision. Therefore, it is difficult to minimize the damage which the members suffer from the collision.
The present invention has been made with the aim of solving the above problems, and it is an object of the present invention to provide a drive-controlling method for precisely detecting a collision of a driven member being driven by a driver such as a robot with an obstacle, and for keeping damages of the members from the collision minimum, and to provide a drive-controlling apparatus using the method and a robot having the apparatus.
The drive-controlling method of the present invention for detecting a collision of a driven member being driven by a driver with a obstacle, and for controlling to subdue a damage of the driven member suffered from the collision, is characterized in that it comprises steps of: storing a driving route of the driven member; and controlling the driver such that the driven member leaves a predetermined distance from the obstacle based on the stored driving route of the driven member before the collision is detected.
The drive-controlling apparatus of the present invention for detecting a collision of a driven member being driven by a driver with an obstacle, and for controlling to subdue a damage of the driven member suffered from the collision, is characterized in that it comprises: a route storing memory for storing a driving route of the driven member; and a controller for controlling the driver such that the driven member leaves a predetermined distance from the obstacle based on the stored driving route of the driven member before the collision is detected.
Therefore, the driven member (movable part) of the driver (robot) is not kept pushing against the obstacle when the driven member collided with the obstacle and thus a damage which the member suffers from the collision is minimized.
In the above invention, a reference level of detecting the collision of the driven member with the obstacle may be set based on operational data of the driver which is obtained by actually driving the driven member. Therefore, accurate collision detection is made possible in accordance with actual operational environment of the driver.
In the above invention, in the case that the driven member is a robot arm, it may be considered that the collision is detected when a current value or a rate of change in the current value of a servo motor driving the arm exceeds the reference level.
In the above invention, in the case that the arm have a plurality of axes which are driven by independent servo motors, each axis may be driven either under a reversing process or a forwarding process when the collision is detected. The reversing process is to drive corresponding axes to a direction opposite to the direction before the detection of the collision. The forwarding process is to drive corresponding axes to a direction same as the direction before the detection of the collision. Here, a comparison is made between a logical current value of the corresponding servo motor and a resultant in which the logical current value is subtracted by an actual current value of the servo motor. If those two values show opposite sign, the reversing process is executed; and if those two values show the same sign, the forwarding process is executed.
Therefore, since the axes which are driving the driven member in a direction away from the obstacle when a collision is occurred is controlled to be driven in the same direction, it is possible to avoid aggravating a degree of damage, for example, which is suffered from re-pushing the driven member against the obstacle when reversing the driving direction of the axes toward the obstacle.
In the above invention, the above mentioned reversing process may be to control the arm to leave from the obstacle for a predetermined distance back along a predetermined section of the route.
In the above invention, the predetermined distance may be set to be constant nevertheless of a speed of the driven member before the collision is detected.
In the above invention, the apparatus is explained as if independent from the robot or the arm thereof; however the apparatus may be included in the robot.